Mercury 850 No Start After Impeller Change

sebagoboater

Cadet
Joined
Jun 30, 2016
Messages
7
So I received a boat with a Mercury 850 70's vintage on it. I replaced some fuel lines and got it running. It was stuck in gear though but ran fine. I decided to fix the gear issue. I took the lower unit off and replaced the impeller put it back up in correctly and adjusted cables. Would now go in FNR great. I started the engine on muffs and it pumped water as it ran. It also was in neutral so i was super excited now. The engine ran for about 1 min and then shut down. I couldn't get it to fire. When I pulled some plugs it appeared there might have been water droplets on them. I sprayed a fuel mixture into each cylinder and it would run on just that. Did that a few times and the plugs were dry after that. I am getting fuel to the carb. I took out the plug on the bottom that accesses the jet where the fuel flows in from the bowl and gas poured right out. Put it back in,pumped the primer. I unscrewed it and gas poured out again. The bulb does stay hard until I drain the carb. It appears that gas isnt getting pulled up through tube. I figured maybe something got clogged up while having the motor tilted way up when i was lining up shift shaft and what not. I have decided to remove carbs to clean/rebuild them. When I fill the bowl full of fuel in my hand and run compressed air through the carb inlet it does siphon the fuel up through the tube. Now this compressed air is obviously passing over a lot faster than if your trying to start the motor. My question I guess is what are the chances that something odd happened when replacing the impeller? Keeping my fingers crossed on rebuilding the carbs. Any ideas or thoughts. I just figured I would put my story out there because it seemed strange. Thanks!
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,146
I would doubt the repair of the waterpump did anything to the motor. Are your choke shutters working? Is there air leakage around the carb bases? Is there a crack in the crankcase cover?

Did you clean the idle restrictor (Merc idle jet terminology) tube? Air the Idle pinholes in the carb throat clean?
 

DeepCMark58A

Commander
Joined
Aug 17, 2015
Messages
2,040
Did you rebuild the fuel pump? If the lines were bad chances are the fuel pump needs some care. Bonus the rebuild is cheap and easy.
 
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